I'm not a printer guy, so this may be a dumb question. All those many models with all their differences and changes - to they not all accept a simple postscript file?

Many decades ago when I was a unix admin, you used to just dump a postscript file to the printer device, and it would print. From a quick google search, every printer I see has postscript drivers - from hp to epson to brother. PS is open, you don't need a driver from the vendor to make a PS file - you can make it with any software you want.

So if this is true (and maybe it's not), then the reason there are no open source printer drivers is because there are, and they've been around always, and the same one will work for all printers, because PS is a standard that's not printer-dependent.